1. School of Computer Science and Technology, College of Intelligence and Computing, Tianjin University, Tianjin, China
2. School of Information Science and Engineering, the Key Laboratory of Software Engineering of Hebei Province, YanShan University, Qinhuangdao, China
3. School of Economics and Management and the Key Laboratory of Software Engineering of Hebei Province, YanShan University, Qinhuangdao, China
4. School of Communication and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing, China
5. School of Computer Science, University of Oklahoma, Norman, OK, USA